Morphometric variability in diatoms
Project description
Diatoms are microscopic algae living in lakes, rivers and oceans. During photosynthesis they produce oxygen, and if you sum it all up, they account for ca. 20 % of the oxygen we breathe, i.e. an amount equal to the one produced by all of the Earth’s rainforests.
As a marine geologist, I am more interested in what happens to them once they die and their „skeleton“, made of biogenic silica (pretty much like glass in composition), gets incorporated in the sediments at the bottom of the ocean.
Scanning Electron Microscope (SEM) pictures of F. kerguelensis valves (scale bar = 10 microns)
In fact, as they fall down through the water column, they export silicon and organic matter to the ocean’s abyss, and therefore a big diatom bloom may reduce the amount of CO2 in the atmosphere, by using it during photosynthesis to build their soft parts, and „sequestering“ it away from the ocean surface.
Massive blooms occur during summer and spring in specific areas of the Southern Ocean, close to the Antarctic Polar Front (in the so-called „opal belt“), and I am looking at the geological record for the most important species in this area: Fragilariopsis kerguelensis.
Geographic distribution of biogenic silica accumulation rates (data from Geibert et al., 2005) and Fragilariopsis kerguelensis valve area (data from Cortese and Gersonde, 2007). High values for both are found in a wide band called the Southern Ocean „opal belt“, located close to the Antarctic Polar Front (purple line in the bottom panel).
Specifically, I want to develop a tool to trace past changes in this area of high export and incorporation of siliceous fossils into the sediment, and the valve size of this species seems to be quite useful in this respect.
What I do is to measure their valves in surface sediments (representative of modern conditions), and see how the average size of this species varies over a large portion of the Southern Ocean. If you compare this distribution to independent estimates of the accumulation of biogenic silica in the sediment, you will notice that large valves correspond to high accumulation rates, thus size in F. kerguelensis can be used to trace the „opal belt“.
Detailed scientific background, and an in-depth description of the Research Center Ocean Margin Project „Linking high to low latitude nutrient cycling to Quaternary climate cycles: A joint geochemical-paleobiological process study“ can be found under this link: http://www.rcom.marum.de/Page3163.html
More information about myself in these pages:
Funding
The Alfred Wegener Institute for Polar and Marine Research (Bremerhaven)
Research Center Ocean Margins (Bremen)
Key publications
Cortese, G., and Gersonde, R. (2007, accepted for publication on Earth and Planetary Science Letters). Morphometric variability in the diatom Fragilariopsis kerguelensis: implications for Southern Ocean paleoceanography
Abelmann, A., Gersonde, R., Cortese, G., Kuhn, G., Smetacek, V. (2006). Extensive phytoplankton blooms in the Atlantic Sector of the glacial Southern Ocean, Paleoceanography.
Cortese, G., Gersonde, R., Hillenbrand, C. -D., Kuhn, G. (2004). Opal sedimentation shifts in the World Ocean over last 15 Myr, Earth and planetary science letters, 224(3-4), 509-527. DOI: 10.1016/j.epsl.2004.05.035